Rate grade and tactical grade silicon inertial angular rate sensors are typically constructed with sensing elements that consist of a suspended silicon resonator excited by an electrostatic motor to produce angular momentum. FIG. 1 illustrates a typical electronic circuit 100 configured to sense a capacitance value and convert the capacitance value to a voltage proportional to the input rate. The electronic circuit 100 may comprise a microstructure 110 in communication with a rate summer 120, where the rate signal is amplified by a charge amplifier 130. The electronic circuit 100 may further comprise a demodulator that receives a signal from the charge amplifier 130 and sends a demodulated signal to a quadrature reduction circuit 150. When the electronic circuit 100 is subjected to an input angular rate, the need to change the angular momentum forces a displacement to occur along a sense axis that is measured through the change in an integral capacitor of microstructure 110. By controlling the motor amplitude, the angular momentum is held constant, which produces a linear displacement when subjected to an angular rate along the input axis.
Angular momentum may be produced in a silicon resonator when a suspended mass is in motion. When an electrostatic motor is used to produce this motion, the resulting angular momentum is at maximum when the angular velocity is at a maximum and the motor displacement is at a minimum. Rate sensing occurs when angular momentum is at a maximum which corresponds to a 0° phase lead relative to the motor displacement. This may be referred to as the in phase component of the total rate signal AC waveform and is typically very small compared to the overall rate signal. The other component of the total rate signal is the quadrature component, which should be minimized in order to allow for greater signal to noise ratios in the in phase signal. The rate signal may be extracted from the in phase signal by down converting or demodulating the rate signal using the motor displacement signal as the phase reference.
Moreover, rate grade and tactical grade silicon inertial angular rate sensors are typically subject to many error sources which limit performance and may make it difficult to use for high accuracy applications. These include large total rate signal relative to the in phase signal, electronic noise in the interfacing electronics, resolution of the A/D converter, phase jitter in the demodulator, phase jitter in the motor frequency, motor drive signal coupling into the rate signal, nonlinearity of the restoring forces, and hysteresis from die mounting stress.
In contrast, a navigation-grade rate sensor provides signal power far above the noise floor such that low noise and navigation grade bias stability can be achieved. A navigation-grade rate sensor (gyro) may be a Hemispherical Resonator Gyro (HRG), and quartz-based for accuracy. However, a HRG is typically more expensive, fragile, and larger than a rate or tactical grade silicon inertial angular rate sensor. Further, a HRG uses a resonant frequency that is temperature dependent and thus varies based on the microstructure temperature. The temperature variance is another aspect that may be compensated for in the prior art design, leading to additional complexity.